This invention relates to a self-processing film unit which is used for an instant camera, and more particularly to an improvement of a leakage preventing structure of a self-processing film unit for preventing the leakage of surplus developing solution or processing solution from an air venting passage.
In a monosheet self-processing film unit (herein-after simply referred to as a "film unit") which is integrally formed of a photosensitive sheet, a mask sheet, a cover sheet, etc., a processing solution container is ruptured by spreading rollers after the photosensitive sheet has been exposed and a processing solution contained in the container is spread between the photosensitive sheet and a cover sheet over a predetermined width while pushing air from the film unit so as to be discharged from the air venting passage. One example of such an air venting passage is described in Japanese Patent Appln. No. Sho 63-156165. Although this Japanese application is not yet laid open, the general principles taught therein can be seen from the accompanying FIG. 14.
As seen in FIG. 14, this earlier arrangement is characterized in that an adhesive agent is applied to a mask sheet 2 in such a manner as to form a pattern thereon such that a portion with no adhesive agent applied thereto is formed on what is otherwise the adhering surfaces of the mask sheet 2 and the cover sheet 4. The portion with no adhesive agent applied thereto does not adhere to cover sheet 4 and so serves to define an air venting passage 5. Reference numeral 6 represents a photosensitive sheet.
In this earlier construction, when the processing solution 7 is spread, a surplus of processing solution is generated, although the quantity of such surplus processing solution is comparatively small. Such surplus processing solution forms a pool in a folded portion of the mask sheet 2. As is shown by arrows in FIG. 14, most of such surplus processing solution is caught by a trapping member 1, but a part of it reaches the inner end of the air venting passage 5 after passing through a gap between the trapping member 1 and the cover sheet 4. Although this surplus processing solution will ultimately be absorbed by the trapping member 1 and hardened, some time is required until the solution is completely absorbed. Therefore, although the surplus processing solution has a high viscosity immediately after it is spread, the solution nevertheless still has the possibility to flow. If a photographer carelessly grasps the nearby area of the trapping member 1 after processing, the surplus processing solution pooled in the vicinity of the air venting passage 5 sometimes leaks out through the air venting passage 5.